The smell of wood smoke reminds me of dressing for school in front of the fire on cold Michigan mornings. Fireplaces and woodstoves were part of winter when I was growing up, and there's a certain romance to the smell of wood smoke in cold air that makes me want to inhale deeply.

Carbon monoxide interferes with the delivery of oxygen throughout the body, can cause symptoms that are sometimes confused with the flu or food poisoning, and can cause death at high concentrations.

Nitrogen dioxide irritates mucous membranes in the eye, nose and throat and may increase the risk of respiratory infection. Particles can carry a number of pollutants, including some that cause cancer, deep into the lungs.

While central heating has replaced the need for a hearth, visible fire still satisfies a primal need. Here are some important precautions:

Just as you have your central heating system checked by a professional every year, you also should have your fireplace, chimney and/or wood stove checked annually.

When you have a fire, the fireplace flue should be fully open and draw all of the smoke outside.

When there is no fire -- the hearth is stone cold, no embers, no glow, no warm ashes -- the flue should be tightly closed to keep warm air inside and cold air outside.

Now let's look at sources of carbon monoxide and nitrogen dioxide we don't usually think about.

Do you have a gas range or gas oven? Make sure they are properly adjusted and vent directly to the outdoors. The flame should be all blue; yellow means it is not burning clean and needs some adjustment. It's a good idea to run the exhaust fan whenever you use a gas stove or oven, especially with windows closed. If you have a gas dryer, make sure the vent to the outside is clear, not blocked by lint or small critters, and be sure to clean the lint screen often.

Generators should be placed outdoors and never used inside a structure. Always open the garage door before you start your car.